a. The Field of the Invention
This invention is concerned with the art of producing and making use of prefabricated strip material adapted to be laid on and adhesively secured to the pavement of highways and other roadable areas to form on said areas traffic regulating signs and markings, such as traffic lane dividing lines, parking areas defining lines, pedestrian crossing signalling strips and the like.
B. The Prior Art
This art is a well known and worked one and extensive comments thereabout are unnecessary. The strip material is primarily designed to form at selected areas on the roadway pavement neatly visible markings of such color (generally white or light) in sharp contrast with that (generally dark) of the adjacent surface of the pavement, the visibility of the markings requiring that the upper face of the marking strip will not be dirt-retentive. Further a good nighttime visibility at distance, when the marking is illuminated by the vehicle headlamps only, is greatly desirable, and therefore the provision of suitably retro-collimating elements on its said upper face is wanted. Still further, the marked area, that is the upper face of the strip face of the strip material laid on and secured to the roadway pavement, forms a portion of the roadable area and, therefore, said material must resist to most severe abuse and provide a desirably long service-life, and also be firmly secured to its substratum, that is the roadway pavement or, preferably, a generally bitumen-based "primer" layer preliminary laid and doctored on said pavement to provide a water impervious and smooth surface best suitable for laying and adhering the strip material thereon.
A number of patents and patent publications related to the art to which this invention appertains have heretofore been made open to public inspection. The most of the problems involved in this art have been extensively discussed in the U.S. Pat. Nos. 3,399,607 and and 3,782,843 of the United States of America, to the present Applicant. An advantageous manner for retro-reflecting "grazing" light (that is the light emitted by vehicle headlamps and which impinges on the marked area in a direction forming a very small angle with the marked surface) has been described in the other U.S. Pat. No. 3,587,415 to the present Applicant. A more intense optical response to grazing light can be provided by partially embedding in the road marking strip material retro-collimating elements comprising each a transparent spheroidal body having a monolayer of reflectorized tiny beads or of reflectorized concave part-spherical surface partially arranged thereabout, as detailedly explained and illustrated in the British Patent Specification No. 1,343,196, also of the present Applicant.
An important and recent improvement to the art of forming marking strip materials possessing an extremely advantageous resistance to traffic wear, together with non-skid properties, consists of forming at least the upper layer of the strip of polyurethane resin or other synthetic resin having a highest molecular internal cohesion, and of embedding in said upper layer very hard crystals, such of corundum. This latter improvement has been disclosed in the published specifications of the French patent application No. 73-18464 (and German patent application No. 2,326,925).
It has been however experienced that, while it can be said that a number of the problems involved in the provision of a really efficient, durable and satisfyingly economical marking strip material have been individually solved by prior art, a long felt want still exists for a strip material which jointly possesses any of the apparently conflicting desired properties.